Conventionally, a Sn-plated (reflow Sn-plated or bright Sn-electroplated) copper alloy has been used in in-vehicle connectors or the like.
In recent years, in response to demand for space savings in a vehicle cabin, a place where connectors are disposed has been progressively shifted from the inside of the cabin to the inside of an engine room. It is said that the temperature of an atmosphere inside the engine room becomes about 150° C. or higher than that. Accordingly, in a conventional Sn-plated material, Cu and an alloy element from a copper or copper alloy base material are diffused in a surface thereof to form a thick oxide coating in the surface layer of Sn plating, and increase the contact resistance of a terminal contact portion. This causes concerns about heat generation from an electronic control device and an electric current disorder therein.
As a technique for improving the situation, a method has been developed which provides a Ni layer and a Cu—Sn alloy layer between the base material and a Sn plating layer, and thereby prevents the diffusion of Cu from the base material (see Patent Documents 1 and 2). The method allows a low contact resistance value to be maintained at a terminal contact portion even after long-time heating at 150° C. However, the use of the method in a temperature range in excess of 150° C. is avoided.
When heating is performed for a long time at a temperature in excess of 150° C., the speed of Ni diffusion increases and, even in the Sn-plated copper alloy of JP-2004-68026 A and JP-2006-77307 A, Ni is diffused from the valley of the Cu—Sn alloy layer or an extremely thin portion thereof into the Sn layer to form a Ni—Sn intermetallic compound or a Ni oxide in the surface layer of Sn plating, increases a contact resistance value, and causes heat generation and an electric current disorder in the same manner as in the conventional Sn-plated material. As a result, it may be difficult to maintain electric reliability. Accordingly, a plated material has been required in which an increase in contact resistance value and plating separation do not occur even after long-time heating at 180° C.